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World History Unit 4: Transoceanic interconnections (c. 1450–1750)

European maritime exploration created global trade networks, the Columbian Exchange and the Atlantic slave trade.

Covers: Technological innovations, exploration, the Columbian Exchange, maritime empires, the Atlantic slave trade, resistance, changing social hierarchies

Study guide

New maritime technologies made ocean exploration possible: the caravel (a small, maneuverable ship), the lateen sail, the astrolabe and the magnetic compass, many borrowed from Asian and Islamic sailors. Portugal led the way, sailing down Africa's coast; Vasco da Gama reached India in 1498. Spain sponsored Columbus, who reached the Caribbean in 1492. Europeans sought gold, God and glory: wealth from spices and precious metals, the spread of Christianity, and prestige.

The Columbian Exchange moved plants, animals, people and diseases between the Eastern and Western Hemispheres. Smallpox and other diseases killed most of the Indigenous population of the Americas, who had no immunity. Horses, cattle, pigs, sugar and wheat came to the Americas, while potatoes, maize and cassava went to Afro-Eurasia, contributing to population growth there. Spain conquered the Aztecs (Cortés) and the Inca (Pizarro). American silver, especially from Potosí, flowed to Europe and then to China, which demanded silver for taxes, creating the first truly global trade network.

Labor systems changed. Spain used the encomienda (forced Indigenous labor), adapted the mit'a for mining, and later the hacienda system. Sugar plantations in Brazil and the Caribbean depended on enslaved Africans, and the Atlantic slave trade forcibly moved about 12 million Africans across the Middle Passage. Joint-stock companies like the Dutch East India Company financed trade, and mercantilism held that colonies existed to enrich the home country. In the Americas, the casta system ranked people by ancestry, with peninsulares at the top, then creoles, mestizos, mulattoes, Indigenous people and enslaved Africans. Resistance included maroon communities of escaped slaves and the Pueblo Revolt of 1680.

Rather than conquer large territories in Asia, Portugal built a trading-post empire of fortified ports such as Goa, Malacca and Hormuz and forced Indian Ocean ships to buy passes (cartaz). Powerful Asian states like the Mughals and Qing kept Europeans trading on their terms, and China later confined European traders to Canton. Some African states, such as Dahomey and Asante, grew powerful by capturing and selling captives for European guns and goods, while Kongo's king protested the damage the trade caused. Because the trade took mostly young men, it left gender imbalances. Queen Nzinga of Ndongo resisted Portuguese expansion.

Songhai replaced Mali as West Africa's leading empire, centered on cities like Timbuktu and Gao, until a Moroccan invasion in 1591. The flood of American gold and silver lowered the value of West African gold in world markets. Enslaved Africans in the Americas preserved and blended their traditions, creating syncretic religions such as Vodou and Santería, creole languages, and new forms of music and food.

Missionaries, especially Jesuits like Francis Xavier, spread Christianity in Asia. Tokugawa Japan banned Christianity in the early 1600s and expelled most Europeans, and Qing emperors restricted missionaries after disputes over Confucian rites. Spain's Manila galleons carried Mexican silver across the Pacific to the Philippines to buy Chinese silk and porcelain, directly linking the Americas and Asia.

Key ideas

• New ships and navigation tools enabled European ocean exploration.
• The Columbian Exchange moved crops, animals and disease between hemispheres.
• Disease killed most Indigenous Americans.
• American silver created a global trade network linked to China.
• Plantations drove the Atlantic slave trade.

Formulas and rules

Common mistakes

• Thinking war was the main cause of Indigenous population decline; disease was.
• Confusing peninsulares (born in Spain) with creoles (Spanish descent, born in the Americas).

Words to know

Caravel

Small, maneuverable Portuguese ship for ocean exploration.

Astrolabe

Navigation tool that measured latitude using the stars.

Columbian Exchange

Transfer of plants, animals, people and disease between hemispheres.

Potosí

Silver mine in the Andes that supplied much of the world's silver.

Encomienda

Spanish system granting colonists the labor of Indigenous people.

Hacienda

Large Spanish colonial estate.

Middle Passage

The voyage of enslaved Africans across the Atlantic.

Plantation economy

Large farms producing cash crops with enslaved labor.

Joint-stock company

A business owned by shareholders who share risk and profit.

Mercantilism

The idea that colonies exist to enrich the home country.

Casta system

Spanish colonial hierarchy based on ancestry.

Peninsulares

People born in Spain living in the colonies; the top of the casta system.

Creoles

People of Spanish descent born in the Americas.

Mestizos

People of mixed European and Indigenous ancestry.

Maroon communities

Settlements of people who escaped slavery.

Pueblo Revolt

1680 uprising that briefly drove the Spanish out of New Mexico.

Sample practice questions

5 more questions like these, from level 1 to 5, are in the practice set.